Abstract
The electrochemical reduction of CO2 to CO is a promising technology for replacing production processes employing fossil fuels. Still, low energy efficiencies hinder the production of CO at commercial scale. CO2 electrolysis has mainly been performed in neutral or alkaline media, but recent fundamental work shows that high selectivities for CO can also be achieved in acidic media. Therefore, we investigate the feasibility of CO2 electrolysis at pH 2–4 at indrustrially relevant conditions, using 10 cm2 gold gas diffusion electrodes. Operating at current densities up to 200 mA cm−2, we obtain CO faradaic efficiencies between 80–90% in sulfate electrolyte, with a 30% improvement of the overall process energy efficiency, in comparison with neutral media. Additionally, we find that weakly hydrated cations are crucial for accomplishing high reaction rates and enabling CO2 electrolysis in acidic media. This study represents a step towards the application of acidic electrolyzers for CO2 electroreduction.
Highlights
The electrochemical reduction of CO2 to carbon monoxide (CO) is a promising technology for replacing production processes employing fossil fuels
Our work shows that operating in acidic media, in sulfate electrolyte, can considerably decrease the energy costs without harming other important figures of merit such as current density and faradaic efficiencies (FE)
The protons can to some extent neutralize the OH− produced upon reduction of CO2 while in alkaline media these species will be neutralized by CO2 itself, lowering the reactants concentration at the reaction interface
Summary
The electrochemical reduction of CO2 to CO is a promising technology for replacing production processes employing fossil fuels. An important building block employed in large scale for the production of commodity and specialty chemicals is carbon monoxide (CO)[1] It can be produced via the electrochemical reduction of CO2 (CO2R), and, provided the electricity comes from zero emission technologies, the carbon cycle can be closed[2]. A known limitation of the electrocatalytic CO2R is the low solubility of CO2 in aqueous media (33 mM at 1 atm and 25 °C) and the poor transport of CO2 to the catalyst surface[6] This limitation can be overcome with the use of gas diffusion electrodes (GDEs), which are porous structures that contain a gas diffusion layer and a catalyst layer[7]. The local concentration of various species (such as CO2, HCO3−, CO32− OH−, and H+) has shown to play a crucial role on the competition between CO2 reduction and hydrogen evolution, through proton[10,11], bicarbonate[12], or water[13] reduction
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